arm: imx: hab: Make imx_hab_is_enabled global

arm: imx: hab: Make imx_hab_is_enabled global

It will be helpful to boot commands to know if the HAB is enabled. Export
imx_hab_is_enabled() now to facilitate further work with this data-point in
a secure-boot context.

Signed-off-by: Bryan O'Donoghue <[email protected]>
Cc: Stefano Babic <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: Peng Fan <[email protected]>
Cc: Albert Aribaud <[email protected]>
Cc: Sven Ebenfeld <[email protected]>
Cc: George McCollister <[email protected]>
Cc: Breno Matheus Lima <[email protected]>
Tested-by: Breno Lima <[email protected]>
Reviewed-by: Fabio Estevam <[email protected]>